Figure 16 shows the standard "house curve" to
which most theater systems are equalized. Note that it
closely resembles the summed curve shown in Figure
15D, indicating that flat power response systems will
require little, if any, added equalization in most houses.
JBL's theater systems using Bi-Radial horns exhibit
essentially flat power response as well as flat on-axis
response. The smaller systems exhibit flat on-axis
response, but their power response rolls off slightly at
high frequencies. JBL's passive dividing networks pro-
vide for a high-frequency boost which effectively makes
any of the systems power-flat at high frequencies. In the
smaller systems, this may be accompanied by a slight
on-axis rise at high frequencies. Nevertheless, we rec-
ommend that some degree of high-frequency boost be
used in all theater applications.
FIGURE 16. ISO STANDARD PLAYBACK RESPONSE
Data from
Figure 15
G.
Model 3152A Field Network Modification:
correcting the normal power response roll-off of the
compression driver. JBL recommends that the boost be
used in all theater systems.
The model 3152A network has been replaced by the
3160.
There are two important differences between the
old and new models. The impedance of the low-fre-
quency section has been changed from eight to four
ohms,
thus providing a better sensitivity match between
the low and high sections. Further, the new network has
a switch which introduces a high-frequency boost for
There are, however, quite a few of the older 3152A
networks in the
field,
and they can be modified to provide
the required boost. Details for this modification are given
in Technical Note Volume 1, Number 5. Figures 17 and
18 outline that modification for your convenience.
FIGURE 17. 3152A NETWORK MODIFICATIONS
3.6 mH
LF
OUT
6.0 mH
: i8sr
• (10 WATT)
4.7 JUF*
(200
VDC)
20a*
(10
WATT)
HF
OUT
A. SCHEMATIC OF MODIFIED NETWORK
* NEW COMPONENTS
JUMPER
WIRE
B. VIEW WITH COVER REMOVED
21
INPUT
12H
13.5
13.5
10£2
13.5 MF
LF LF HF
INPUT
10
WATT, WIRE-WOUND
RESISTORS IN PARALLEL
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